Various fuels have been identified to mitigate the rising price of energy and environmental concerns. For example, alcohol has been recognized as an attractive alternative source of energy, and more particularly a fuel for automotive applications. Various engine systems may be used with alcohol fuels, utilizing various engine technologies such as turbo-chargers, super-chargers, etc. Further, various approaches may be used to control alcohol-fuelled engines with such devices, including adjustment of boost or spark timing in dependence upon an alcohol content of the engine fuel, and various operating conditions.
The inventors herein have recognized several interrelated issues with alcohol-fuelled engines involving the fuel delivery system, and found that it is possible to operate the engine system to achieve improved engine performance with an alcohol fuel or blend by varying the amounts, timing, and number of injections.
In one example, an engine system is provided for an engine having at least a cylinder and combusting a fuel, the system comprising: a direct injection fuel injector coupled to the cylinder; an intake charge boosting device coupled to the engine and fluidly coupled to the cylinder; and a control system for varying at least a spark timing of the cylinder and boost amount of said device as an alcohol content of the directly injected fuel varies, said system operating the engine to produce increased peak torque output when said alcohol content is increased, at least during one condition.
In this way, it is possible to utilize direct injection and boosting, along with an appropriate boost, spark, and fuel control system, to take advantage of increased charge cooling effects via alcohol's increased heat of vaporization and increased octane to provide an engine with improved peak torque output. In one particular example, peak engine torque, at least for some conditions, can be increased when using a fuel with increased alcohol compared to another fuel with less alcohol content. Such performance can be achieved using the above approach, even though the fuel with increased alcohol may have a reduced energy density.
As such, a customer can be encouraged, rather than discouraged, to utilize alternative fuels as such use can proved improved engine performance. The improved performance can provide various benefits, such as improved towing capacity, improved acceleration, and/or various others.
Further, use of such alternative fuels may also provide reduced emissions and various other environmental and/or economic advantages. For example, use of direct injection fuel can reduce the effect of varying amounts of alcohol on intake system puddling. The improved air-fuel ratio control can then be used to further reduce the likelihood of knock by providing more appropriate spark timing.
In another aspect, improved marketing and/or advertising may be achieved. For example, it may be possible to inform potential consumers that a vehicle having an engine (with one or more of the features described herein) may be able to obtain improved vehicle performance when using a fuel with increased alcohol, rather than simply maintaining performance or achieving degraded performance.